Composite structures made from fiberglass material impregnated with a cured, thermoset resin are known for manufacturing articles such as spas, tubs, recreational vehicles, auto body panels, and marine components such as boat decks and hulls. The composite structures are sometimes referred to as fiberglass reinforced articles.
Conventional methods for making fiberglass reinforced articles involve manually shaping the glass fiber to a mold surface and then impregnating the glass fiber with a thermoset resin. Two common techniques for fiberglass reinforced article structures comprising a fiberglass reinforced composite material impregnated with a cured, thermoset resin can be referred to as open molding and closed molding.
In both open molding and closed molding techniques, a gel coat of clear or pigmented thermoset resin is typically applied to the surface of a mold before forming a final laminate structure. The gel coat results in a smooth, cosmetically attractive surface for the finished article and protects the fiber composite from attack by ultra violet radiation from the sun. Materials selected for use as a gel coat on the exterior surface of the composite require a combination of desirable properties including outdoor weatherability, impact resistance, attractive cosmetic qualities, and ease of processing. Gel coats are typically applied to the mold surface by spray methods in which the material in thickened liquid form is placed on the mold surface.
During an open molding process, a combination of glass fiber and resin is typically applied over the gel coat. The combination of glass fiber and resin is often applied as a spray through a chopper gun. The fiberglass can be referred to as long strand fiberglass or chopped fiber, and the resin is often a polyester resin containing volatile organic components (VOCs) such as styrene monomer. As the polyester resin cures, the VOCs are released to the environment. Many of these volatile components are classified as hazardous air pollutants that are harmful to human health and the environment. Further, VOCs are often flammable resulting in a fire hazard. Elaborate precautions and expensive equipment can be used to reduce the release of and exposure to these volatile substances. As a result of open molding, however, substantial amounts of VOCs are typically released.
Closed mold processes were developed to reduce the emission of VOCs. Exemplary closed mold processes can be referred to as reaction injection molding and resin transfer molding. Reaction injection molding and resin transfer molding are processes wherein dry fiber reinforcement plys or panels sometimes referred to as engineered glass fiber are loaded in a mold cavity having surfaces that define the ultimate configuration of an article. Using engineered glass fiber requires skill and patience in cutting and trimming the plys or panels and placing them in the mold so that they sufficiently cover the mold cavity. Molds having a curved surface, such as, boat hull molds, typically require the cutting and trimming of the engineered glass fiber to provide complete coverage over the mold surface to avoid open spaces and to avoid overlap. Furthermore, it is often necessary to apply an adhesive to the engineered glass fiber so that it remains in place covering the mold surface. Preforms generally require steps of forming the preform on a screen where the glass fiber cures, and then transferring the preform to the mold An exemplary technique showing the formation of preform is described by GB 2 015 915 A. Once the engineered glass fiber or preform is placed in the mold, a second mold half can be placed over first mold half forming a mold cavity or plenum containing the engineered glass fiber or preform. A flowable resin is injected into the mold cavity or plenum to impregnate or saturate the engineered glass fiber. After a period of curing, the finished article is removed from the mold plenum. An advantage of the closed mold process is that emission can be significantly reduced compared with the open mold process. Compared with chopped fiber however, the engineered glass fiber is typically substantially more expensive. Furthermore, the use of engineered glass fiber is more time consuming and requires more man hours to place within a mold. In addition, the preparation of a preform requires additional time and space in order to allow the preform to cure before the preform is introduced into the mold.
While it is desirable to reduce the emissions associated with the open mold process, it is also desirable to reduce the costs associated with the use of the closed mold process. As a result, alternative processes have been developed. One method disclosed in U.S. Pat. No. 6,030,575 applies a heated binder to fibers already supported on a support surface while a vacuum is applied to the other side of the support surface. By this method, the fibers are held in place by the vacuum while the binder is applied at a high pressure by a spray device. This application applies pressure to the fibers thus forming a solid reinforcing structure. Upon application, and with the assistance of the air flow from the vacuum, the binder cools and solidifies into the desired preform shape. However, the application of the vacuum requires additional equipment in the form of a plenum arrangement and also requires additional control functions and labor to properly apply the fibers and vacuum. Therefore, the material and operating costs are increased. Another technique utilizes an open flame as a heating source to melt the binder mixed with glass fiber that is sprayed onto a mold and, as a result, provides robotics for applying the spray of binder and glass fiber. For example, see U.S. Patent Publication Nos. US 2006/0163772 and US 2005/0161861.